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gprs: Fix LLC UI window 

According to TS 44.064 section 8.4.2, the LLC layer should only
drop UI frames if V(UR)-32 <= N(U) < V(UR).  The code was dropping
frames whenever N(U) < V(UR).  Consequently, large amounts of
packets could be dropped if, e.g., V(UR)==511 and the frame with
N(U)==511 was lost.  All frames would be dropped until the next
time a frame with N(U)==511 is received.
This commit is contained in:
Jonathan Santos 2011-06-23 17:53:27 -04:00
parent 7ad066c5c3
commit 5f7d3cd6d2
1 changed files with 15 additions and 11 deletions
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26
src/gprs/gprs_llc.c
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@ -482,17 +482,21 @@ static int gprs_llc_hdr_rx(struct gprs_llc_hdr_parsed *gph,
}
break;
case GPRS_LLC_UI:
if (gph->seq_tx < lle->vu_recv) {
LOGP(DLLC, LOGL_NOTICE, "TLLI=%08x dropping UI, vurecv %u <= %u\n",
lle->llme ? lle->llme->tlli : -1,
gph->seq_tx, lle->vu_recv);
return -EIO;
}
/* Increment the sequence number that we expect in the next frame */
lle->vu_recv = (gph->seq_tx + 1) % 512;
/* Increment Overflow Counter */
if ((gph->seq_tx + 1) / 512)
lle->oc_ui_recv += 512;
{
int delta = (lle->vu_recv - gph->seq_tx) & 0x1ff;
if (0 < delta && delta < 32) {
LOGP(DLLC, LOGL_NOTICE, "TLLI=%08x dropping UI, vurecv %u <= %u\n",
lle->llme ? lle->llme->tlli : -1,
gph->seq_tx, lle->vu_recv);
return -EIO;
}
/* Increment the sequence number that we expect in the next frame */
lle->vu_recv = (gph->seq_tx + 1) & 0x1ff;
/* Increment Overflow Counter */
if (lle->vu_recv == 0) {
lle->oc_ui_recv += 512;
}
}
break;
}